The present invention relates to a mechanism for actuating a platen in a printer.
More particularly, the invention is concerned with a mechanism for actuating a platen in a printer which is adapted to print a line of printing simultaneously on a paper. The actuating mechanism includes a plurality of rotatable printing rings which are temporarily arrested independently from each other so as to locate selected characters thereon at a printing position which is set in the printer. Also, the platen is abutted against the printing rings, and it is temporarily held or arrested against movement with the paper interposed therebetween to effect a printing onto the paper.
The prior art printer of the type described above is provided with a mechanism for actuating the platen in synchronism with a driving means for rotating the printing rings in order to move the platen towards and away from the printing rings at the same speed so that sufficient time is provided to affect a printing onto the paper. Therefore a delay must be provided to assure that the platen is not positively moved away from the printing rings before effecting a release of the temporary arresting of the printing rings so that the printed paper will not be damaged due to the rotation of the printing rings as a result of a premature releasing thereof.
Further, electromagnets are provided to control the select levers of the printer which in turn controls printing rings with characters thereon. These printing rings must be stopped so as to locate selected characters at the printing position response to the actuation of electromagnets. In order to increase the printing speed, these electromagnets must be deenergized or energized in a very limited or short time period. However, this is not possible with the prior art printer because there are unavoidable time lags, i.e. so-called response time, until the select levers are actually actuated after the magnets are deenergized or energized for the actuation of the select levers. Therefore, the printing speed can not be raised unless the capacity of each magnet is increased or the size of the gears for driving the respective printing rings is made large. In order to raise the speed twice as high as the speed at present, the response time must be reduced to one-fourth of the response time at present which is very difficult to be achieved, and, if the size of the gears is made large, the overall size of the printer is made necessarily large thereby rendering the printer to be less marketable.
The present invention aims at avoiding the above described disadvantages of the prior art printers.